li li
2018-Nov-08 03:55 UTC
[R] Identify row indices corresponding to each distinct row of a matrix
Hi all,
I use the following example to illustrate my question. As you can see,
in matrix C some rows are repeated and I would like to find the indices of
the rows corresponding to each of the distinct rows.
For example, for the row c(1,9), I have used the "which" function to
identify the row indices corresponding to c(1,9). Using this approach, in
order to cover all distinct rows, I need to use a for loop.
I am wondering whether there is an easier way where a for loop can be
avoided?
Thanks very much!
Hanna
> A <- matrix(c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16),8,2)> B <-
rbind(A,A,A)> C <- as.data.frame(B[sample(nrow(B)),])> C V1 V2
1 1 9
2 2 10
3 3 11
4 5 13
5 7 15
6 6 14
7 4 12
8 3 11
9 8 16
10 5 13
11 7 15
12 2 10
13 1 9
14 8 16
15 1 9
16 3 11
17 7 15
18 4 12
19 2 10
20 6 14
21 4 12
22 8 16
23 5 13
24 6 14> T <- unique(C)> T V1 V2
1 1 9
2 2 10
3 3 11
4 5 13
5 7 15
6 6 14
7 4 12
9 8 16> > i <- 1 > which(C[,1]==T[i,1]&
C[,2]==T[i,2])[1] 1 13 15
[[alternative HTML version deleted]]
Bert Gunter
2018-Nov-08 05:20 UTC
[R] Identify row indices corresponding to each distinct row of a matrix
A mess -- due to your continued use of html formatting. But something like this may do what you want (hard to tell with the mess):> m <- matrix(1:16,nrow=8)[rep(1:8,2),] > m[,1] [,2] [1,] 1 9 [2,] 2 10 [3,] 3 11 [4,] 4 12 [5,] 5 13 [6,] 6 14 [7,] 7 15 [8,] 8 16 [9,] 1 9 [10,] 2 10 [11,] 3 11 [12,] 4 12 [13,] 5 13 [14,] 6 14 [15,] 7 15 [16,] 8 16> vec <- apply(m,1,paste,collapse="-") ## converts rows into charactervector> vec[1] "1-9" "2-10" "3-11" "4-12" "5-13" "6-14" "7-15" "8-16" "1-9" "2-10" "3-11" "4-12" "5-13" "6-14" [15] "7-15" "8-16"> ## Then maybe: > tapply(seq_along(vec),vec, I)$`1-9` [1] 1 9 $`2-10` [1] 2 10 $`3-11` [1] 3 11 $`4-12` [1] 4 12 $`5-13` [1] 5 13 $`6-14` [1] 6 14 $`7-15` [1] 7 15 $`8-16` [1] 8 16> ## gives the row numbers for each unique rowThere may well be slicker ways to do this -- if this is actually what you want to do. -- Bert On Wed, Nov 7, 2018 at 7:56 PM li li <hannah.hlx at gmail.com> wrote:> Hi all, > I use the following example to illustrate my question. As you can see, > in matrix C some rows are repeated and I would like to find the indices of > the rows corresponding to each of the distinct rows. > For example, for the row c(1,9), I have used the "which" function to > identify the row indices corresponding to c(1,9). Using this approach, in > order to cover all distinct rows, I need to use a for loop. > I am wondering whether there is an easier way where a for loop can be > avoided? > Thanks very much! > Hanna > > > > > A <- matrix(c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16),8,2)> B <- > rbind(A,A,A)> C <- as.data.frame(B[sample(nrow(B)),])> C V1 V2 > 1 1 9 > 2 2 10 > 3 3 11 > 4 5 13 > 5 7 15 > 6 6 14 > 7 4 12 > 8 3 11 > 9 8 16 > 10 5 13 > 11 7 15 > 12 2 10 > 13 1 9 > 14 8 16 > 15 1 9 > 16 3 11 > 17 7 15 > 18 4 12 > 19 2 10 > 20 6 14 > 21 4 12 > 22 8 16 > 23 5 13 > 24 6 14> T <- unique(C)> T V1 V2 > 1 1 9 > 2 2 10 > 3 3 11 > 4 5 13 > 5 7 15 > 6 6 14 > 7 4 12 > 9 8 16> > i <- 1 > which(C[,1]==T[i,1]& > C[,2]==T[i,2])[1] 1 13 15 > > [[alternative HTML version deleted]] > > ______________________________________________ > R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see > https://stat.ethz.ch/mailman/listinfo/r-help > PLEASE do read the posting guide > http://www.R-project.org/posting-guide.html > and provide commented, minimal, self-contained, reproducible code. >[[alternative HTML version deleted]]
Jeff Newmiller
2018-Nov-08 06:32 UTC
[R] Identify row indices corresponding to each distinct row of a matrix
Perhaps which( ! duplicated( m, MARGIN=1 ) ) ? (untested) On November 7, 2018 9:20:57 PM PST, Bert Gunter <bgunter.4567 at gmail.com> wrote:>A mess -- due to your continued use of html formatting. > >But something like this may do what you want (hard to tell with the >mess): > >> m <- matrix(1:16,nrow=8)[rep(1:8,2),] >> m > [,1] [,2] > [1,] 1 9 > [2,] 2 10 > [3,] 3 11 > [4,] 4 12 > [5,] 5 13 > [6,] 6 14 > [7,] 7 15 > [8,] 8 16 > [9,] 1 9 >[10,] 2 10 >[11,] 3 11 >[12,] 4 12 >[13,] 5 13 >[14,] 6 14 >[15,] 7 15 >[16,] 8 16 >> vec <- apply(m,1,paste,collapse="-") ## converts rows into character >vector >> vec >[1] "1-9" "2-10" "3-11" "4-12" "5-13" "6-14" "7-15" "8-16" "1-9" >"2-10" >"3-11" "4-12" "5-13" "6-14" >[15] "7-15" "8-16" >> ## Then maybe: >> tapply(seq_along(vec),vec, I) >$`1-9` >[1] 1 9 > >$`2-10` >[1] 2 10 > >$`3-11` >[1] 3 11 > >$`4-12` >[1] 4 12 > >$`5-13` >[1] 5 13 > >$`6-14` >[1] 6 14 > >$`7-15` >[1] 7 15 > >$`8-16` >[1] 8 16 > >> ## gives the row numbers for each unique row > >There may well be slicker ways to do this -- if this is actually what >you >want to do. > >-- Bert > > > >On Wed, Nov 7, 2018 at 7:56 PM li li <hannah.hlx at gmail.com> wrote: > >> Hi all, >> I use the following example to illustrate my question. As you can >see, >> in matrix C some rows are repeated and I would like to find the >indices of >> the rows corresponding to each of the distinct rows. >> For example, for the row c(1,9), I have used the "which" function >to >> identify the row indices corresponding to c(1,9). Using this >approach, in >> order to cover all distinct rows, I need to use a for loop. >> I am wondering whether there is an easier way where a for loop can >be >> avoided? >> Thanks very much! >> Hanna >> >> >> >> > A <- matrix(c(1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16),8,2)> B <- >> rbind(A,A,A)> C <- as.data.frame(B[sample(nrow(B)),])> C V1 V2 >> 1 1 9 >> 2 2 10 >> 3 3 11 >> 4 5 13 >> 5 7 15 >> 6 6 14 >> 7 4 12 >> 8 3 11 >> 9 8 16 >> 10 5 13 >> 11 7 15 >> 12 2 10 >> 13 1 9 >> 14 8 16 >> 15 1 9 >> 16 3 11 >> 17 7 15 >> 18 4 12 >> 19 2 10 >> 20 6 14 >> 21 4 12 >> 22 8 16 >> 23 5 13 >> 24 6 14> T <- unique(C)> T V1 V2 >> 1 1 9 >> 2 2 10 >> 3 3 11 >> 4 5 13 >> 5 7 15 >> 6 6 14 >> 7 4 12 >> 9 8 16> > i <- 1 > which(C[,1]==T[i,1]& >> C[,2]==T[i,2])[1] 1 13 15 >> >> [[alternative HTML version deleted]] >> >> ______________________________________________ >> R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see >> https://stat.ethz.ch/mailman/listinfo/r-help >> PLEASE do read the posting guide >> http://www.R-project.org/posting-guide.html >> and provide commented, minimal, self-contained, reproducible code. >> > > [[alternative HTML version deleted]] > >______________________________________________ >R-help at r-project.org mailing list -- To UNSUBSCRIBE and more, see >https://stat.ethz.ch/mailman/listinfo/r-help >PLEASE do read the posting guide >http://www.R-project.org/posting-guide.html >and provide commented, minimal, self-contained, reproducible code.-- Sent from my phone. Please excuse my brevity.